The present invention is directed to the field of solar collectors and more specifically solar collectors with parabolic trough and other types of concentrators.
Solar energy has taken a prominent position in addressing the increasing need for non-polluting alternative sources of energy. Currently, there are four principal means for tapping solar energy. They are (1) parabolic trough concentrators, (2) heliostats (3) photoelectric cell modules, and (4) flat plated hot water collectors. Among these, large arrays of parabolic trough concentrators have become increasingly popular. These arrays, which cover many acres, are typically used to create steam that is then used to generate electricity. The electricity is then pumped into the power grid for distribution elsewhere. This process, however, has several limitations, including significant losses of energy in the conversion of solar energy into electricity and losses in transmitting electricity from the solar arrays to the points of usage.
Applicant proposes herein a simple and practical means for harvesting solar power directly at the point of usage, which include buildings and other structures constructed with parabolic roofs and/or canopies with integral parabolic trough or other solar concentrators that provide on-site solar energy for heat, hot water, and air conditioning, in addition to electricity. Because these structures are essentially immobile, and the path of the points of focus of a solar parabolic trough concentrator move with diurnal and seasonal changes, these solar concentrators or preferably the receivers associated therewith should include self-tracking systems that maintain the receiver in the concentrator's path of the points of focus.
A number of patents have been issued that are directed to solar tracking systems and specifically ones that incorporate photovoltaic cells therein. These include: U.S. Pat. No. 4,031,385 issued to Zerlaut et al., U.S. Pat. No. 4,098,264 issued to Brokaw, U.S. Pat. No. 4,068,653 issued to Bourdon et al., U.S. Pat. No. 4,153,039 issued to Carroll, and U.S. Pat. No. 4,349,733 issued to Beam, which are hereby incorporated herein by reference. The photovoltaic cells in these patents, however, face directly towards the sun. As a result, these cells generate insufficient energy to independently operate the tracking motor of these systems and these systems therefore limit use of the electricity generated with these cells for signal purposes only. As a further result, these systems are not usable at locations where there is no external source of electricity.
Moreover, although U.S. Pat. No. 4,469,938 issued to Cohen, which is also hereby incorporated herein by reference, focuses the photovoltaic cells downward into the parabolic trough concentrator, the '938 patent is designed primarily to move a lightweight aluminized Mylar film concentrator. Although the '938 patent's system is scalable to some extent, the ability of the ability of the tracking solar cells to move the entire reflector places a practical limit on the size of the concentrator. This patent seeks to overcome that limitation by using the tracking solar cells to move the collector pipe instead of the reflector.
Accordingly, there is a need for self-tracking parabolic trough and other solar concentrator systems that are not reliant on external sources of energy to power their tracking motors. There is also generally a need for self-tracking solar concentrator systems that are simple and therefore less expensive to produce, even in large scale systems.